661021390 has 16 divisors (see below), whose sum is σ = 1200960432. Its totient is φ = 261937024.

The previous prime is 661021373. The next prime is 661021399. The reversal of 661021390 is 93120166.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661021399) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 307819 + ... + 309958.

It is an arithmetic number, because the mean of its divisors is an integer number (75060027).

Almost surely, 2^661021390 is an apocalyptic number.

661021390 is a deficient number, since it is larger than the sum of its proper divisors (539939042).

661021390 is a wasteful number, since it uses less digits than its factorization.

661021390 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 617891.

The product of its (nonzero) digits is 1944, while the sum is 28.

The square root of 661021390 is about 25710.3362482874. The cubic root of 661021390 is about 871.1076700339.

The spelling of 661021390 in words is "six hundred sixty-one million, twenty-one thousand, three hundred ninety".